Generator for electric pulsations of audio-frequency



June 26, 1951 E. M. JONES 2,558,653

GENERATOR FOR ELECTRIC PULSATIONS OF AUDIO-FREQUENCY Filed Aug. 6, 1949 IN VEN TOR. [awn/ 0 M :Jmu-s 1:16.61 n'r-ronruavs wllallllollllji Patented June 26, 1951 GENERATOR FOR ELECTRIC PULSATIONS OF AUDIO-FREQUENCY Edward M. Jones, Cincinnati, Ohio, assignor to The Baldwin Company, Cincinnati, Ohio, a corporation of Ohio Application August 6, 1949, Serial No. 108,946

21 Claims.

Y My invention relates to generators for tone and voices useful in electric musical instruments,

and in particular to photoelectric generators for such tones and voices.

One of the objects of the invention is the provision of a photoelectric tone generator as a single, self-contained unit, capable of producing all of the tones required in the range of an electric musical instrument of the keyboard variety. It is an object of my invention to provide a self-contained generator of this class capable of producing a wide variety of voices. A generator assembly which, as a self-contained unit, is capable of producing in a photocell a wide range of tones and tone colors I hereinafter refer to as a complete generator.

It is an object of my invention to provide a complete generator as an individual, self-contained unit, which is simple and inexpensive.

It is an object of my invention to provide a complete generator which contains all of the moving parts and motive means required in the production of the said tones and tone colors, the complete generator requiring only connection to the keys of a keyboard instrument and the stops thereof, together with electrical connections to a power source and to one or more amplifiers and loud speakers. Thus, it is an object of my invention to provide a complete generator which can be installed and replaced as a unit in an elec-,

trical musical instrument.

It is an object of my invention to provide a complete generator with a minimum of moving parts.

It is an object of my invention to provide a complete generator which is protected from extraneous influences including dust and dirt which would interfere with its operation.

It is an object of my invention to provide a complete generator in which the replacement and repair of individual parts is greatly facilitated.

These and other objects of my invention which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, I accomplish by that construction and arrangement of parts of which I shall now describe an exemplary embodiment. Reference is made to the accompanying drawings wherein:

Figure 1 is a top plan view of my complete generator with certain parts of the casing broken away.

Figure 2 is a vertical sectional view of my complete generator taken along the section line 22 of Figure 1. a

Figure 3 is an elevational view of my complete generator.

Figure 4 is a top plan view of simplified and semi-diagrammatic character of a base and shutter plate which I may employ.

Figure 5 is a partial sectional view taken along the line 5--5 of Figure 4 and showing a mode of actuating a tone color shutter.

Figure 6 is a partial sectional view through my pitch disc showing one mode of attachment of an armature element thereto.

It has hitherto been understood that if light from a source is broken up into spaced, moving beams following each other at an audio frequency corresponding to a note of the musical scale, it is possible to produce a voice or voices of any desired timbre by causing the moving beams of light to pass through wave form representations whereby they are modified as to harmonic content before the beams are caused to impinge on a photoelectric cell. The wave form representations have a length equivalent to the spacing on centers of the moving beams of light; there may be a plurality of wave form representations in consecutive order so that a plurality of the beams may be simultaneously modified for the purpose of admitting more light to the photoelectric cell and of smoothing out sporadic Variations in the several wave form representations; and the series of wave form representations for modifying the several beams will be optically limited in extent so that as one beam begins to be modified by the representations, another leaves them to avoid in the produced tones alterations of the harmonic content represented by the wave forms. Moving beams of light will be provided for all of the desired frequencies within the range of the instrument; wave form representations for modifying the various sets of moving beams will be provided for each voice throughout the range of frequencies desired for that voice; and different sets of wave form representations throughout the range of the instrument or such portions of that range as may be desired, will be provided for each of the voices desired in the instrument, with arrangements for causing the several sets of moving beams to traverse these various wave form representations selectively or in desired combinations. These principles are employed in the generator structure herein described. Theoretically, the principles outlined above when translated into a physical structure should provide an inexpensive and simple generator for musical tones for use in keyboard instruments, as compared with other types of generators, say electromechanical, or thermionic. The great mass of complex electrical wiring in instruments using such other forms of generators is of course eliminated. The

tones, selected in accordance with the actuation of the playing keys, and modified as to voice in accordance With the actuation of stop tabs, are collected at the photocell; and it is only necessary to amplify and translate int sound the output of the photocell by means of a suitable amplifier and loud-speaker system. However, the theoretical advantages of this type of structure have not hitherto been attained in practice. The

proposed assemblies have been complicated and unwieldy, have included mechanical coupling problems substantially as difficult as the electrical Wiring problems of instruments using other types of generators, and in most instances have contemplated duplications of apparatus even for the production of that range of tones and voices required in a single manual instrument. Furthermore, the assemblies of apparatus hitherto proposed have been highly complex, liable to come out of. adjustment, susceptible to failure in operation due to mechanical damage or the accumulation of dust and dirt, and have been difficult to assemble, disassemble and repair.

- In the apparatus hereinafter described, I provide a complete generator assembly as a self -contained unit, sealed against access of dirt and dust, having but one driven moving part, of simple and inexpensive construction, with all parts easily accessible for repair or replacement, and with the whole unit readily removable should this be required. In this way, and in others which will be set forth hereinafter, I have obtained a structure wherein the theoretical advantages of the photoelectric type of operation can be fully realized.

The self-contained, complete generator unit hereinafter described can readily be made to produce all of the frequencies desired throughout the entire range of the instrument including high frequencies which may be desired primarily for coupling purposs. tain all of the frequencies required for a single keyboard plus a number of other frequencies which may be the same or may be octavely related, and which are appropriate for use, for example, in connection with a pedal keyboard. It is possible by varying the shutter arrangement to provide a single complete generator in accordance with my pattern which will serve more than one manual of an organtyp instrument together with a pedal keyboard; but in the more elaborate I double manual instruments where a great variety of different voices may be desired, it is readily possible to install two of my complete generating units connecting one with each of the manuals, and both with the pedal keyboard or portions thereof. Due to the inexpensive character of my assembly, this may readily be done without un-- duly increasing cost.

Briefly, in the practice of my invention I provide a main or base plate on which all other elements of the assembly are mounted, either directly, or by means of housing elements which engage the base plate and serve as a complete dust-tight cover for all of the active elements of the structure. Thev main or bas plate of the apparatus is perforated for the passage of light. A source of light is located upon one side of it, and a photoelectric cell is located upon the other. Preferably the base plate is a shutter plate; and Iprefer to employ a type of shutter construction in accordance with the general principles set forth in the copending application of John F. Jordan, entitled Shutter Mechanism, Serial No. 45,897, filed August 24, 1948, and now Patent No. 2,506,599.

It may, indeed, be made to con- In this copending application, Jordan described a structure having the advantage of including a very large number of shutter openings and shutters in a very small space, together with additional, or common shutter means whereby light from the source could be permitted to pass through any one or more of various series of primary light openings extending throughout the full tonal range or such portions thereof as may be desired, the last mentioned shutter means serving to select the voices as will hereinafter be made clear. The Jordan shutter plate comprised in. an exemplary form, a disc-like member such as that illustrated diagrammatically at l in Figur 4 of this application. One surface of the plate is provided with a series of closely spaced grooves 3 in each of which is placed a wire element 4. The grooves are deep enough to contain the wire elements, and have a width substantially double that of the thickness of the wire elements. At one side of each of the grooves a deeper groove is cut, substantially half the width of the main groove. Channel-like configurations as at 6 are molded or cut into the other side of the shutter plate. They intersect the last mentioned, narrow, deeper grooves and thus provide series of light openings indicated in Figur 4 at l. The wires 4 lying in the main grooves are adapted to cover or uncover these light openings; and they do this by flexing in response to either a push or pull exerted on the wires longitudinally as may be desired, one end of the wires being anchored as at 8. The channels 6 may be arranged radially or otherwise; but they traverse either the entire series of grooves or desired groups thereof; and there will be located in connection with each of the several series of light openings 1, a series of wave form representations as hereinafter set forth. Figure 4 is diagrammatic in that the number of wires and main grooves has been diminished for the purpose of a simplified showing. I have found it readily possible to provide in a shutter plate having'a diameter of approximately fifteen inches a series of grooves great enough in number to accommodate all of the 73 notes desired for a single-manual organ, or all of the 61 notes desired for a given manual in a two-manual organ plus 12 or 13 others, as may be desired for connection with a pedal manual. The shutters themselves are simply operated by pushing or pulling uponthe wires 4; and this is most conveniently done by providing Bowden transmissions, so-called, in connection with each. These transmissions comprise inner wires 4a, connected to the wires 4, in sheaves 9 anchored as at 9a. The grooves on the. one side of the plate are interrupted in an area indicated generall at ill; but. the rim of the plate may be continued as at H. The sheaves 9 of. the Bowden transmissions may be passed through holes l2 in this rim. The Bowden transmissions may be prolonged as desired, and only require connection directly or indirectly with the playin keys of the instrument for actuation. It will be noted that the actuation of a single wire will open up a plurality of apertures in the shutter plate, say one for each of the voic channels or slots 6. In this way, voices may readily be combined in my instrument.

Each of the voice channels or slots 6, will, as shown in Figure 5 be provided with a hinged shutter l3, which also may be actuated by a wire l4 passing through a sheave l5 and forming a Bowden transmission. These last mentioned Bowden transmissions are initially located with the stop shutter devices l3 on the under side of my plate I. In the space I0, however, I may pro-- vide an opening I6 through which the stop transmission elements [5 may be brought into the space In on the upper side of the shutter plate and then lead therefrom through perforations I! in the rim II, as shown in Figure 1. Again as shown in Figures 2 and 3 the transmissions I5 may be brought through transverse perforations in a channel engagin an edge of the lower can or housing hereinafter described. The Bowden transmissions I5 require only to be connected directly or indirectly with the stop tabs of the musical instrument, as will be understood. It will be clear that, when a voice shutter I3 is open, light responding to any of the frequencies for which there is a groove on the shutter plate traversed by the voice slot will be allowed to pass through one or more of the light openings 1 depending upon the actuation of one or more of the wires 4 by the playing keys of the instrument.

Juxtaposed to the shutter disc which I have been describing, there will be a plate or disc having concentric series of light openings in it, one for each of the frequencies desired, this disc, here inafter called the pitch disc, i indicated at I8 in Figures 1 and 2. The pitch tracks thereon are diagrammatically indicated at I9 in Figure 1. Also juxtaposed to the shutter plate there is a voice disc (28, in Figure 2) which will bear wave form representations in a plurality of series, a series corresponding to each of the voice channels or slots 6 hereinabove described.

. The specific construction of the shutter plate herein above described is not a limitation upon the present invention. The shutter plate may be modified as specifically set forth in my copending application entitled Method and Means for Producing Tones and Voices Photo-Electrically, Serial No. 117,239, filed September 22, 1949, wherein specific provision is made for octave coupling by means of the wires constituting the shutter elements, and wherein particular arrangemens of the voice slots 6 are set forth and claimed.

Also, particular arrangements of the pitch tracks on the pitch disc I8 and the voicing representations on the voice disc are not limitations on the present invention. Preferably their arrangement is that set forth in my copending application referred to above. The teachings of the present application relate to the novel combination and mechanical arrangement of elements as hereinafter taught and claimed, irrespective of variations in the physical details of the elements themselves, excepting as these may be included in the appended claims.

As indicated, the shutter plate I is the base plate or main plate of my construction. It is designed to be supported as such in the console 'of a musical instrument in any way, and on any particular means desired. To this end I have shown, in an exemplary fashion, ears formed on the plate for mounting purposes. Other means may be substituted as will be apparent, such as mounting brackets bolted to the plate, or the like.

Centrally of the shutter plate I, I provide a bearing holder 22. The pitch diSc I8 (usually and preferably a plate of glass, the pitch tracks being photographic representations thereon) is provided with a central perforation engaged by a hub 23 and a clamping flange 24. The hub 23 has a central, downwardly depending shaft 25'. There is a thrust bearing, preferably a ball bearing 26, located between the hub 23 and the bearing holder 22; and at the lower end of the bearing holder there is a centering ball bearing in- 6 dicated at 21. The pitch disc, mounted as described, is the only driven elment in my structure. The proportioning of the parts is such that the pitch disc is maintained parallel to and in close proximity to the shutter plate I but it will be seen from Figure 2 that the voice disc 28 rests directly on the shutter plate, its centered position being maintained by the bearing holder 22 which engages a central perforation in the voice disc 20. The voice disc 28 is also preferably a disc of glass, bearing voice representations which are.

photographic in nature. That the sets of voice or timbre representations on the voice disc 2') correspond in position to the voice channels or slots 6 will be clear without special illustration. The voice disc 20 may serve to maintain the wires 4 in the slots 3, as shown, or separate means may be provided for this purpose. Clamping means for the voice disc (not shown) may be provided to maintain its radial position.

The remaining apparatus elements going to make up my complete generator assembly are mounted or supported from the base plate I' by means of housing elements or cans. There is an upper can indicated generally at 28 and a lower can 29. These cans may be formed of sheet metal or other suitable material. Both are generally circular in shape excepting that they are generally flattened at one side as at 30 and 3|. The upper can, however, has an extension indicated at 32 so that it is able completely to house the pitch disc I8. This extension may be integral with the upper can, or as shown, it may be formed as a separate member of any suitable construction, such, for example, as a die casting, and provided with a, lower rim 33 responding to the rim II on the plate, and with side and top channels 34 and 34a to accept edge portions of the can 28, with a packing material to make the joints dust-tight.

There are various ways in which the cans may be attached to the plate. The upper can may be formed with a peripheral flange corresponding to the upper side of the rim II on the base plate I. It may be held to the rim by means of bolts or otherwise, and if desired a gasket may be placed between the flange and rim so as to further the dust-tightness. The lower can 29 may be similarly shaped and fastened, However, I provide merely to rabbet the edges of the plate I for the acceptance of contacting edges of the cans, as most clearly shown in Figure 2, fastening the can edges in place by means of screws. Noncontacting edges of the upper can 28 are held, as above noted, in the channels 34 and 34a of the extension element 32. To accept the edge of the flattened portion 3| of the lower can 29, I prefer to mold or machine a channel 36 on the underside of the plate I.

The lower can 29 contains a light source 31, usually and preferably in the form of an incandescent bulb. The bulb has a socket 38 which is preferably mounted in a removable housing element 39 extending through the wall of the lower can and provided with fins 40 for heat dissipation purposes. The front end of the housing 39 may be formed as at 4| to shield the shutter plate I from the direct rays of the lamp 31. Means for adjusting the position of the lamp within the housing 39 may also be provided as desired. The direct rays of the lamp 3'! pass downwardly and impinge upon a reflector 42. This reflector is half of a parabolic reflector which may be made of metal or silvered glass and is mounted in the lower can 29 by means 01.

suitable'brackets 43. and padding 44. Theiparat-v belie-reflector alters the direction of the light pass through the openings in the shutter plate. land the representations on the voice and pitch These rays pass upwardly to. another half of a parabolic reflector, indicated.

discs 20 and Id.

at 45, mounted in the upper can 28 on brackets. 46 and padding 4?, and serving to focus the rays which pass through the shutter plate I, voice disc 20' and pitch disc 18 on a photocell indicated at 48- in Figure 2'. The mounting of the photocell will hereinafter be described.

The pitch disc in my structure is preferably directly driven by electromotive means. I prefer, but am not limited to, an eddy current motor. I provide the pitch disc It with a perhipheral, upstanding armature element indicated at 49 in Figure 6. This is made up of convolutionsior windings of some non-magnetic metal such. as: It may be fastened to the copper or aluminum. periphery of the Voice disc in any suitable. way. One way, which I prefer, is illustrated in Figure 6. The convolutions making up the armature 49 motor which I prefer to use comprise an inner structure having a C-shaped core 56 and a windingl (see Figure 1). This structure is supportedirom the extension 32 of the upper can by means of bolts 52 and sleeves, in a position such that the ends of the C-shaped core 50 are in close proximity to the armature 49.

core 53 and winding 5%. These elements are supported on and housed by the upper can extension'32', this extension having a protuberance 55 for the purpose. The motor element is mounted therein by means. of bolts 56 sothat the ends of the core legs are in close proximity, as.

The coils 5| and-'54 shown, to the armature 59. will be energized by alternating current in any way desired. Speed control and prcvisionsfor: variation of the speed to provide a vibrato, may be incorporated in this structure as set forthin the copending application of Edward M. Jones. and George F:Wi1liamson entitled Systems for the. Production and Use of Electric Pulsations for: Control Purposes, Serial No. 117,240 filed Sep-- tember 22, 1949.

The photocell 43 may be mounted in a suitable socket 51 on a bracket 58 afiixed to the inside.-

of the flattened portion 30 of the upper can 28;

The socket will be so positioned as to support the photocell E8 at the focus of the rays from the upper parabolic mirror t5;-

or other circuit devices useful in connection withv the photocell l8 and such speed control circuit elements as may be desired in connection with the windings 5| and 54 of the eddy current motor used for driving the pitch disc.

In Figure l, I have shown at H! a speed-control track 78 and a vibrato track H on the pitch disc- IB; Light from the source 37 passes through There is also. an outer motor element comprising an E-shaped' The bracket 58 may also support elements indicated generally at 59, which elements may include a preamplifier I tion to a source of power.

appropriate. openings: in. the plate 1,. thence; through theseetracks; and impinges on another photocell 'I2Iwhich is alsomounted. on: the bracketu5'8i The various connections from the electrical elements in the upper can 23 may be brought.

outto-a pronged connector ea (or a socket) mounted in the-flattened portion 3i! of the upperv with leads 61 for the application of power and thesemay be provided with a plug-in connec- Also the housing 39. for the light' sourcc may be removed as such from the lower can, and without removing the lower can, since it-is held thereto by bracket means 62'. Either can may be removed for'repair'orreplacement without disturbing any other part'of the apparatus, as will be evident. The connections-to the'playing keys and to the stops run only to the base plate I as will also be clear; but the complete generator may be removed from the console of an instrument by disengaging these connections and disengaging the ears 2i from-thesupporting means within the console.

The apparatus assembly is simple; it has'as indicated'above only one driven part namely the pitch disc [8; it can be made inexpensively but Withgreat accuracy; it can be very small in size for the number of frequencies and voices producible'by'it; it is completely enclosed and dustti'g-ht although readily accessible for repair or replacement, and it requires no electrical wir-- i'ngexcepting for connections to a source of power and to an amplifier and loud speaker system.

'Modifications may be made in my invention without departing from the spirit of it. Having thus described my invention in an exemplary embodiment, What I claim as new and desire to secure by Letters Patent'is:

1. In a generator, a base plate having openings for the passage of light, a bearing holder mountedsubstantially centrally on said base plate, a

shaft mounted on bearings in said bearing holder, a 'hub on said shaft and a pitch disc mounted on said hub and lying in proximity to and adjacent a" surface of said base plate.

2; In a generator, a base plate having open ings for the passage of light, a bearing holder mounted substantially centrally on said base plate, a'shaft mounted on bearings in said bearing holder, a hub on said shaft and pitch disc mounted on said hub and lying in proximity to and adjacent a surface of said base plate, and means for rotating said pitch disc supported from said base plate.

1 3. In a generator, a base plate having openings for the passage of light, a bearing holder mounted substantially centrally of said base plate, a shaft mounted on bearings in said bearing holder, a hub on said shaft and a pitch disc mounted on said hub and lying in proximity to and adjacent asurface of said base plate, and means for rotating said pitch disc supported from said base plate, and comprising an annular armature mounted substantially peripherally on said pitch disc and an electromagnet acting on said armature.

' 4. The structure claimed in claim 3 wherein housings are removably attached to either side of said base plate, one of said housings containing and supporting a light source and the otfier' containing and supporting'a' photoelectric. ce

'5. The structure claimed in claim: 3 wherein housings are removably attached to either side of said base plate, one of said housings contain ing and supporting a light source and the other containing and supporting a photoelectric cell, said light source and photoelectric cell being in substantial axial alignment with said shaft, and said housings also containing reflectors serving to pass light from said light source through openings in said main plate and to focus the said light on said photo cell.

6. The structure claimed in claim 5 wherein said housings have flattened sides, wherein said light source is mounted in a heat dissipating fix-' ture affixed to the flattened side of one of said' housings.

7. The structure claimed in claim 5 wherein said housings have flattened sides, wherein said light source is mounted in a heat dissipating fixture aflixed to the flattened side of one of said housings, and wherein said electromagnet constitutes together with said armature an eddy current motor and comprises a C-shaped core and winding mounted interiorly of said armature and an E-shaped core and winding mounted exteriorly thereof, both cores being mounted to the housing supporting said photoelectric cell and included therein, said housings forming with said main plate a dust-tight construction. ,5}. The structure claimed in claim 5 wherein said housings have flattened sides, wherein said light sourceismounted in a heat dissipating fixture afixed to the flattened side of one of said housings, and wherein said electromagnet con-' stitutes together with said armature an eddy current motor and comprises a C-shaped core and winding mounted interiorly of said armatureiand an E-shaped core and winding mounted exteriorly thereof, both cores being mounted to the housing supporting said photoelectric cell and included therein, said housings forming with said main plate a dust-tight construction, said annular armature being substantially cylindrical in formation and extending substantially normal to the periphery of said pitch disc.

9. The structure claimed in claim 5 wherein said housings have flattened sides, wherein said light source is mounted in a heat dissipating fixture aflixed to the flattened side of one of said housings, and wherein said electromagnet constitutes together with said armature an eddy current motor and comprises a c-shaped core and winding mounted interiorly of said armature and an E-shaped core and winding mounted exteriorly thereof, both cores being mounted to the housing supporting said photoelectric cell and included therein, said housings forming with said main plate a dust-tight construction, said annular armature being substantially cylindrical in formation and extending substantially normal to the periphery of said pitch disc, and being laminated in construction and formed from a winding of non-magnetic strip metal, certain of the convolutions thereof engaging a surface of said pitch disc and at least one convolution extending beyond said surface and crimped against a beveled edge of said pitch disc whereby to fasten said armature to said pitch disc.

10. The structure claimed in claim 2 wherein said main plate is a shutter plate having substantially concentric grooves in its surface lying adjacent said pitch disc, wires lying in said grooves, and acting as shutter elements for said light openings which open into said grooves, the

said surface of said main plate having a depressed portion formed by an'interruption of said grooves and terminating outwardly in a raised rim, said wires beingconnected to actuating wires which change direction in said; depressed portion and pass outwardly periph erally of said plate through openings in said rim, one end of each of said first mentioned wires: being anchored to said main plate.

11. The structure claimed" in claim 2 wherein. said main plate is a shutter platelhaving substantially concentric grooves in its surface lying adjacent said pitch disc, wires lying in said grooves, and acting'as shutter elements for said light openings which open into said grooves, the: said surface of said main plate having a de pressed portion formed by an interruption of said: grooves and terminating outwardly in a raised rim, said wires being connected to actuating: wires which change direction in said depressed; portion and pass outwardly'peripherally of said plate through openings in said rim, one end of each of said first mentioned wires being anchored to said main plate, said actuating Wires where. they pass through said rim and therebeyond being surrounded by sheaths.

12. The structure claimed in claim 2 wherein said main plate is a shutter plate having sub-=7 stantially concentric grooves in its surface lying adjacent said pitch disc, wires lying" in said grooves, and acting as shutter elements for said light openings which open into said grooves, the said surface of said main plate having a depressed portion formed by an interruption of said grooves and terminating outwardly in a raised rim, said; wires being connected to actuating wires which change direction in said depressed portion and; pass outwardly peripherally of said plate throughopenings in said rim, oneend; of each ofsaid first mentioned wires being anchored to said main plate, said actuating wires where they pass through said rim and therebeyond being surrounded by sheaths, and a voice disc lying against the grooved surface of said main plate and substantially closing the grooves therein.

13. The structure claimed in claim 12 wherein the said substantially concentric grooves have narrower grooves extending inwardly from their bottom portions and wherein said last mentioned grooves are intersected by channels formed in the opposite face of said base plate so as to intersect said grooves, thereby providing said light openings.

14. The structure claimed in claim 12 wherein the said substantially concentric grooves have narrower grooves extending inwardly from their bottom portions and wherein said last mentioned grooves are intersected by channels formed in the opposite face of said base plate so as to intersect said grooves, thereby providing said light openings, and wherein said channels are provided with shutters operated by wire-and-sheath transmissions, and wherein said last mentioned transmissions pass outwardly from said plate through a dust-tight exit.

15. The structure claimed in claim 12 wherein the said substantially concentric grooves have narrower grooves extending inwardly from their bottom portions and wherein said last mentioned grooves are intersected by channels formed in the opposite face of said base plate so as to intersect said grooves thereby providing said light openings, and wherein said channels are provided with shutters operated by wire-and-sheath transmissions pass outwardl y from said plate througha dust tight exit and inuwhichtsaidpitch disc-and voice dise' ar'ei membersi'of v. transparent material bearing photographic representations respective- 13%" of light" slots arranged concentrically in: accordance With thepitch requirements of a musical scale and locatedopposite said.- light openings I in said: main plate, and voicing representations aligned with the'fseri'es offopenings'iormed in connection with said'channels 16; In-combi nation for the:purpose described ashutter piateiiconstituting a'mounting plate, a voice disc supported by. said shutter: plate; a pitch disc adjacent said voice: disc and rotatively mounted-on said shutter plate, housings detachably mounted to :either-side of said shutter plate; driving means for said pitch disc mounted on one-90f said housings; a light=source and .a photoelectric cell mountedrespectively: on said housings said housingshaving; a: dust-tight relation with said shutter" plate; andishu-tter operating elements passing from saidshutter plate through peripheral 1 openings therein 1 whereby to preserve said' dust-tight construction;

173 The combination claimedinclaim-lfi; including a speed controbtrack-onesaid-pitch-disc and a second photoelectric eel-1 mounted in'the housing, containing said first mentioned photoelectric celL-said second cell being alignedwith said track;

18. In combination for the purpose described, a disc-like: shutter: plate constituting. a mountingplate; a? bearing. holder mounted substantially sourcean'd a photoelectric cell, housings-mounted: to: :either: side oi sa-idshutter plat'erandr en= closing all of the above recited elements excepte ing-iforrportions of said shutter: plate and c0- a'ctingiwith saidshutter plate. to'formra'dusttight construction and strand-like shutterx'opcrating elements entering said dust-tight construction substantially at the level of said shutter plate.

19. Ina generator, abase, plate, .a pitch disc journaled forv rotation onsaid base plate, an: annular armature rim on-said pitch: disc; and electromagnetic driving means forsaid armature supported from said base plate.

20,111 a generator, va base plate,za pitch disc journaled. for rotation on saidibase plate and an. annulararmature.rimzon said pitch disc; saidirim being; of laminated construction, and non-ro tatably fastened to the said pitch disc.

21; The structurev claimed in claimt 20:wherein said armature: is substantially cylindrical in shape and extends substantially? normal to the said pitch disc: at the. periphery? thereof, the laminated construction of. said armature. being convolute, the edges of certain of the :convolutidns engagingga surface. o'f thei pitch? disc and at least oneconvolution: extending beyond: said? surface and crimped against an'otl'ierssurfaceiv portion" of said'ipitch disc;

EDWARD- ONES:

REFERENCE-S: CITED The followingreferences are-oi record in the file of this patent:

UNITED STATES- PATENTS'Y Number Name Date? 1,937,021 Hammond v iNcv.' 28; 1933 1986547 Winch Ja n; 1,319351 2;0 75,-'802 Davis Apr. 6; 193.? 

